Flexible polyurethane foam is used extensively in a variety of applications requiring the unique mechanical, sound absorbing, load-bearing and/or other properties this material provides. Flexible polyurethane foams are made by reaction of at least one polyisocyanate containing isocyanate (NCO) groups with at least one polyol containing hydroxyl (OH) groups in the presence of blowing agent, surfactant, catalyst and other optional additives. The blowing agent most commonly used is water, which reacts with polyisocyanate to form carbon dioxide and polyurea. The polyurea is present along with the polyurethane resulting from the polyisocyanate-polyol reaction.
Flexible polyurethane foams are typically produced using either a slabstock foam manufacturing process or a molded flexible foam manufacturing process. A slabstock flexible foam is typically produced in either a high pressure or low pressure machine having a continuous mixer. Such continuous mixing machines may generally produce 100 pounds or more per minute of slabstock foam. In general, the production of slabstock foam involves the metering of a polyol-containing composition and a polyisocyanate-containing composition from separate feed lines (i.e., streams) via a mixing head having a pin mixer or high shear mixer into a trough. The product begins to froth and rise out of the trough and overflows onto fall plates. On the fall plates, the product continues to rise and contacts a conveyor. The product cures as the conveyor carries it along a length forming the slabstock foam. The conveyors are typically lined with a paper or plastic liner to allow for easy removal of the slabstock foam. As the foam exits the machine, it is cut into large blocks.
In general, a molded flexible foam is typically produced by mixing a polyol-containing composition and a polyisocyanate-containing composition in a metered foam mixing and dispensing unit to form a foam intermediate composition and dispensing the foam intermediate composition into a sufficiently heated mold of desired design. The mold is typically vented to allow for the build up and subsequent release of internal pressure, has two or more sections with provisions for automatic opening and closing, and may be formed from cast, aluminum or any other suitable material. Following the mixing and dispensing steps, the lid of the mold is closed and locked, and the foam intermediate composition is allowed to cure at a sufficient temperature, for a sufficient period of time. A sufficiently heated oven capable of receiving the mold may also be employed during the curing step. Once the curing step has completed, the lid of the mold is opened and the resultant foam product is removed and then transferred to a foam cell-crushing device which is used to apply pressure to the foam product in order to open the cells prior to being processed via other related finished-foam handling systems such as trimming and fabrication. During trimming and fabrication, the foam is converted into a finished product such as an automobile seating cushion.
Typically, slabstock and molded flexible foams are made from a polyether polyol, a polyisocyanate such as toluene diisocyanate, an amine catalyst and a tin catalyst. Polyether polyols traditionally used to make polyurethane foam are generally derived from petroleum-based raw materials. A standard polyether polyol used in the flexible slabstock foam industry is produced by reaction of propylene oxide with glycerin in the presence of alkoxylation catalyst. Functionality, molecular weight and the alkoxide composition of the polyol (or polyol blend) can be adjusted to affect physical and/or processing properties of the foam produced.
The flexible foam industry has witnessed a significant increase in the use of bio-based polyols, which are incorporated into a formulation at the expense of petroleum-based polyether polyol. The ability to claim a level of bio-renewable content within the foam provides a competitive marketing advantage relative to those not incorporating this type of polyol. Additionally, flexible foam manufacturers have the added potential to realize cost savings through extensive use of these polyols since they generally possess a lower raw material cost than standard petroleum-based polyether polyol.
Bio-based polyols are typically natural oil based. The natural oils, with the exception of those oils having hydroxyl functionality (e.g. castor oil, or lesquerella oil), typically lack isocyanate reactive functionality, and must undergo chemical transformation, such as, for example, transesterification with functionalized materials, epoxidation and ring opening, oxidation, ozonolysis, or hydroformylation to add reactive functionality. The added reactive functionality could be any active hydrogen moiety, and is typically hydroxyl groups or amines. There are challenges to the use of natural oils as raw materials for polyols to be used in polyurethane foam products. The mechanical strength properties such as tear strength, tensile strength and elongation (“TTE”) of foams formed from the reaction of functionalized natural oils with isocyanate are typically deteriorated relative to foams made solely from petrochemical polyols. This deterioration of foam properties can be due, at least in part, to the plasticization of the foam by the relatively high aliphatic concentration of the natural oils. The deterioration of foam properties can also be due, at least in part, to the poor reactivity of the functional group due to steric hindrance by the aliphatic chains of the oil, and the incompatibility of the natural oil polyol with the isocyanate. The loss of these physical properties effectively limits the amount of bio-based polyol that can be incorporated into a flexible foam or formulation.
In view of the foregoing, a method that enables the improvement of the mechanical strength properties of flexible foams made from bio-based polyol and the use of higher concentrations of bio-based polyols without resulting in a loss of mechanical strength properties would represent a significant advancement in the art.